A method for preparing a highly grafted multifunctional olefin copolymer is known from U.S. Pat. No. 6,107,257, which describes the grafting of an ethylenically unsaturated carboxylic acid material onto a copolymer prepared from ethylene and at least one C3 to C23 alpha-olefin and, optionally, a polyene, wherein an intermediate copolymer has grafted thereon from 0.3 to 0.75 carboxylic groups per 1000 number average molecular weight units of olefin copolymer. Next, the polymer intermediate is reacted with a polyamine compound, resulting in an imidized copolymer, wherein the copolymer has a number average molecular weight of between 20,000 and 150,000 g/mol.
A drawback of this known process for preparing a highly grafted multifunctional olefin copolymer is that it requires a low molecular weight polymer to start with.
Another drawback of this known process is that the conversion to the imidized polymer is not more than about 80%. This means that about 20% of the anhydride groups will not be converted to imide groups. In the presence of water, these anhydride groups will be partly or totally converted to acid groups. Another part of the anhydride groups may be converted to amides. Such low degree of conversion requires a higher content of polymer to obtain sufficient dispersancy properties of the oil, which deteriorates the low temperature viscosity of the oil.
An object of this invention is to provide a process for the preparation of a solid novel highly grafted, multi-functional olefin copolymer composition without the above-mentioned drawbacks.
Another object of the invention is to provide a highly grafted, multi-functional lubricant additive effective for imparting viscosity index, dispersancy and antioxidant properties to a lubricating oil composition, as well as enabling extended lubricant drain intervals and improving fuel economy and fuel economy durability.
A further object is to provide a novel lubricating oil composition containing the highly grafted, multi-functional olefin copolymer additive of the invention as well as to provide concentrates of the novel additive of the invention.